As a measure to reduce the nitrogen oxides (NOx) contained in the exhaust gas of a diesel engine, there is conventionally known an EGR valve device, which is an exhaust gas passage valve, for performing so called EGR (Exhaust Gas Recirculation) in which a part of the exhaust gas generated by the engine is returned to the intake system of the engine for recirculation (refer to, for example, Patent Document 1 and Patent Document 2).
EGR valve is not only exposed to the high temperature exhaust gas introduced from exhaust pipe, but also exposed to the exhaust gas cooled by a recirculation exhaust gas cooler and therefore having reduced temperature. Fine particles such as carbon exist in the exhaust gas, and the carbon will deposit on the valve stem of the EGR valve. Further, in the exhaust gas having reduced temperature, since sulfuric acid will be generated from the sulfur content in fuel, corrosion by the sulfuric acid will occur, and the carbon will further deposit on the corroded part to cause the fixing, so that operation failure of the EGR valve will possibly occur.
As shown in FIG. 10, the exhaust gas recirculation control valve 105, which is an EGR valve device, disclosed in Patent Document 1 includes a housing having an exhaust gas passage thereinside, a control valve 106 for adjusting the quantity of the exhaust gas flowing through the exhaust gas passage of the housing, in which a stem 117 holding the control valve 106 is provided to freely slide in a guiding member 114 having a penetrating hole. A holder 131 for forming a predetermined space for the stem 117 is provided on the control valve side of the guiding member 114 provided in the housing. Further, metal scrubber filler 130 contacting the circumference of the stem 117 is provided inside the predetermined space of the holder 131, and the carbon deposited on the stem 117 is wiped off by the metal scrubber filler 130 while the stem 117 is sliding.
Further, the EGR valve device disclosed in Patent Document 2 includes, as shown in FIG. 9, a housing 112 having an exhaust gas passage 113 thereinside, a valve element 116 for adjusting the quantity of the exhaust gas flowing through the exhaust gas passage 113 of the housing 112, in which the valve element 116 freely slides via a valve guide 115.
A hydraulic actuator 118 for opening and closing the valve element 116 is provided in the upper portion of the housing 112. The hydraulic actuator 118 consists of a cylinder 119 and a piston 120 provided to freely slide inside the cylinder 119. The hydraulic actuator 118 works by moving the piston 120 with the pressured oil supplied from a solenoid valve 133 through an oil sending line 132.
Further, the EGR valve device is provided with a cooling and lubricating section 135 for cooling and lubricating the valve guide 115 and the like by the supplied pressured oil. The cooling and lubricating section 135 is constituted by, corresponding to the stroke of the piston 120 in the valve opening direction, an oil passage 136 which connects a front chamber 119a of the piston 120 and a spring chamber 127, the spring chamber 127 functioning both as a cooling oil jacket and as a lubricating oil reservoir, and an outlet port 137 for discharging the oil from the spring chamber 127. The oil passage 136 is formed by grooving the inner circumference of the cylinder 119 along the axial direction thereof.
On the one end side of the oil passage 136, when the piston 120 moves to the position P1 indicated by dashed line at full stroke, it opens at the front chamber 119a by a predetermined area, and the pressured oil introduced from the front chamber 119a can be introduced toward the periphery of the valve guide 115 as shown by the arrow.
When the EGR valve device is in operation, the pressured oil forcedly fed by the oil pump (not shown) is sent to the hydraulic actuator 118 by the solenoid valve 133. The piston 120 performs stroke driven by the pressured oil, and as a result the pressured oil introduced into the spring chamber 127 returns to the oil pan from the outlet port 137 after being flowed in contact with the periphery of the valve guide 115 and a stem 116a. Thus the heat of the valve guide 115 and the stem 116a is taken by the pressured oil flowing therearound and emitted to the out, and therefore the valve guide 115 and the stem 116a are prevented from overheating.
[Patent Document 1]: Japanese Patent Laid-Open Publication No. Hei11-336616.
[Patent Document 2]: Japanese Patent Laid-Open Publication No. Hei07-332169 (Page 3-4, FIG. 1, and FIG. 2).